It is known in the art that R-value is a measure of the insulating characteristics of a window. In particular, R-value is the reciprocal of U-value. In other words, U value=1/R-value. The term U-value or U-factor (synonymous with thermal transmittance) is well understood in the art and is used herein according to this well known meaning. U-value herein is reported in terms of BTU/hr/ft2/degrees F., and may be determined accorded to the guarded hot box method as reported in and according to ASTM designation C1199-91 (incorporated herein by reference). Similarly, R-value is the reciprocal of U-value as explained above.
The R-value for a monolithic glass sheet (one sheet of glass) is typically around 1.0. Moreover, the R-value for an insulating glass (IG) unit with two sheets of uncoated glass spaced apart from each other is typically about 2.0 (i.e., U value of about 0.5). When one of the glass sheets of an IG unit is coated with a low-E (low emissivity) coating, the R value can be increased (e.g., to about 3 or 4). Argon gas between the glass sheets of an IG unit can also increase R-value (and thus decrease U-value).
Conventional IG units often use metal spacer(s) as the edge of the units to space the glass sheets from one another. However, this causes U values to be higher (and thus R values to be lower) at the edges of such IG units due to the conductivity of the metal spacer(s). It would be advantageous to avoid the use of metal spacers at edges of a glass-based window unit, thereby reducing conductivity of the spacing structure. Plastic spacers have been used previously to address this problem, but have resulted in gas (e.g., Ar) leakage through the plastic thereby leading to durability and insulating problems.
In certain example embodiments of this invention, a window unit may be provided which does not necessarily need a metal spacer in an IG unit. In certain example embodiments, a window sash has a spacer function/structure which may be of plastic or the like; e.g., vinyl or some other polymer based material. Thus, in certain example embodiments, part of the sash may separate two glass sheets of the window from one another.
In certain example embodiments of this invention, a window unit may include a vacuum IG (VIG) unit as an inboard lite and a monolithic lite (e.g., with a low-E coating thereon) as an outboard lite. A dead air space may separate the inboard and outboard lites. Moreover, in certain example embodiments, a highly insulated frame may be used to support the inner and outer lites. The VIG unit may be partially embedded or supported (e.g., by from about 1-6 inches, more preferably from about 1 to 3 inches, with an example being about 2 inches) in the insulating frame, so that the insulating frame separates the VIG unit inboard lite from the outboard lite thereby reducing conductivity around the edges of the window unit so that R-value can be increased (and U-value increased). In certain example embodiments, the edges of the inboard and outboard lites may be vertically offset from one another, to further reduce conductivity at edges portions. In certain example embodiments, the total R-value of the window unit is at least about R-8, and more preferably at least about R-10 (compared to the much lower R-values of conventional IG units).
In certain example embodiments, there is provided a window unit comprising: an insulating frame in which a vacuum IG unit and a monolithic lite are provided, the vacuum IG unit including first and second spaced apart glass sheets that are separated from one another via a gap that is a pressure less than atmospheric, and the monolithic lite being spaced apart from the vacuum IG unit; wherein the frame comprises insulating material that separates the vacuum IG unit from the monolithic lite.
In other example embodiments of this invention, there is provided a window unit comprising: an insulating frame in which both an inboard glass lite and an outboard glass lite are partially embedded, the inboard lite comprising a vacuum IG unit including first and second spaced apart glass sheets that are separated from one another via a gap that is a pressure less than atmospheric, and the outboard lite comprising a monolithic glass sheet spaced apart from the vacuum IG unit; wherein the frame comprises insulating material that separates the outer surface of the vacuum IG unit from the inner surface of the monolithic glass sheet; and wherein along at least one of a top edge, a bottom edge, and/or a side edge of the window unit, the outer edge of the monolithic glass sheet is vertically offset from the outer edge of the vacuum IG unit so that the outer edge of the vacuum IG unit is closer to a periphery of the window unit than is the outer edge of the monolithic glass sheet.